Figure 3-9. - Cylinder heads.

of aluminum since it needs the ability to dissipate large amounts' of heat. On air-cooled engines, the oil pan usually is made of cast aluminum, and it is covered with cooling fins. The oil pan on an air-cooled engine plays a key role in the removal of waste heat from the engine through its lubricating oil.

Cylinder Head

The cylinder head (fig. 3-9) provides combustion for the engine cylinders. It is built to conform to the arrangement of the valves: L-head, I-head, or others.

Cylinder heads on liquid-cooled engines have been made almost exclusively from cast iron until recent years. Because weight has become an important consideration, a large percentage cylinder heads now are being made from aluminum. The cylinder heads on air-cooled engines are made exclusively from aluminum. This is due to the fact that aluminum conducts heat approximately three times as fast as cast iron. This is a critical consideration with air cooling.

In liquid-cooled engines. the cylinder (fig. 3-10) head is bolted to the top of the cylinder block to close the

Figure 3-10. - Cylinder head for L-head engine.